HomeMy WebLinkAboutDrainage Reports - 03/10/2025FDP DRAINAGE REPORT
The Ellie at Old Town North
Tract A, Old Town North Fifth Filing
FDP240015
for:
Van Horn Development Management, LLC
14143 Denver West Parkway #100
Golden, CO 80401
engineer:
TJC Limited
8751 E Hampden Ave, Suite B10, Denver, CO 80231
James W. Allen, PE
303.489.3346
www.tjcivil.com
February 19, 2025
City of Fort Collins Approved Plans
Approved by:
Date:
Derek Lutz
03/10/2025
Final Drainage Report
Page 2 of 10
TABLE OF CONTENTS
GENERAL LOCATION AND EXISTING SITE INFORMATION ............................................. 4
MASTER DRAINAGE BASIN INFORMATION ........................................................................ 4
FLOODPLAIN INFORMATION .................................................................................................. 5
PROJECT DESCRIPTION ............................................................................................................. 5
PROPOSED DRAINAGE FACILITIES ........................................................................................ 5
DRAINAGE DESIGN CRITERIA................................................................................................. 8
VARIANCE REQUESTS ............................................................................................................... 9
EROSION CONTROL ................................................................................................................... 9
CONCLUSION ............................................................................................................................... 9
REFERENCES ............................................................................................................................. 10
APPENDICES .............................................................................................................................. 10
Final Drainage Report
Page 3 of 10
I hereby attest that this report for the final drainage design for the Ellie at Old Town was
prepared by me or under my direct supervision, in accordance with the provisions of the Fort
Collins Stormwater Criteria Manual. I understand that the City of Fort Collins does not and will
not assume liability for drainage facilities designed by others.
James W. Allen Licensed Professional Engineer State of Colorado No. 42256
Final Drainage Report
Page 4 of 10
GENERAL LOCATION AND EXISTING SITE INFORMATION
a) Site Location Description
i. The site is located in Section 1, Township 7 North, Range 69 West of the 6th Principal
Meridian, County of Larimer, State of Colorado. Also known as Tract A, Old Town
North 5th Filing.
ii. A vicinity map is attached in appendix A.
iii. The property is adjacent to Sungia Rd, Blondel St, and Alleys.
iv. Adjacent land uses are residential Old Town North filings.
v. The project is within North East College Corridor Outfall (NECCO) Basin 810. The
project is with Old Town North Third Filing Basin 7.
vi. The existing site generally slopes west to east. There are two existing 18” RCP culverts
that outfall the site under Blondel Street. These culverts were constructed for interim
flows during the development of the area. These flows were eliminated when the NECCO
improvements were completed.
The Old Town North Third Filing drainage report (appendix D) indicates the downstream
facilities were sized to accept 5.1 cfs from the parcel (Basin 7).
vii. There are no irrigation facilities on-site.
viii. The land is currently vacant.
ix. The property is covered with natural grass. Slopes range from 2% to 7%.
x. Soils consist of Nunn clay loam with Hydrologic Soil Group C. A NRCS Soils
Classification Map is attached as appendix C.
MASTER DRAINAGE BASIN INFORMATION
a) The site is located in the Lower Dry Creek Basin. The site was situated in the Dry Creek
floodplain when the original Old Town North plat was recorded in 2004 and Old Town North
was developed. The Dry Creek floodway has since been redefined to remove a majority of
the site from the Dry Creek floodplain. The immediate area adjacent to the property is fully
developed with residential use.
i. The subject property is within the Old Town North Third Filing and 2009 NECCO
study. The project runoff will conveyed through existing stormwater facilities to the
NECCO Detention pond north of Sungia Road.
ii. NECCO assumed a 90% imperviousness (developed condition).
b) Site Drainage Basins
i. The site is composed of one historic sub-basin and no offsite sub-basins:
Sub-basin H1 – consists of grass covered vacant land. Runoff sheet flows east to the
existing 18” RCP culverts under Blondel St.
The Old Town North Third Filing drainage report (appendix D) indicates the downstream
facilities were designed to accept 5.1 cfs from this parcel (Basin 7).
Final Drainage Report
Page 5 of 10
Point (acres) Runoff Runoff
c) There are no irrigation facilities on or adjacent to the property.
FLOODPLAIN INFORMATION
a) The site is within a Zone X according to FEMA Flood Insurance Rate Map No.
08013C0411K (appendix B).
b) The site was situated in the Dry Creek floodplain when the original Old Town North plat was
recorded in 2004 and Old Town North was developed. The Dry Creek floodway has since
been redefined to remove a majority of the site from the Dry Creek floodplain.
PROJECT DESCRIPTION
a) The project proposed two apartment buildings with tuck under garages. Surface parking is
being provided on the west end of the site. The existing alley will be widened. A rain garden
in proposed to meet Ft Collins LID requirements.
b) The site is approximately 0.81 acres.
PROPOSED DRAINAGE FACILITIES
a) The project site is composed of four sub-basins and no offsite sub-basins:
Sub-basin A – consists of roof, pavement, and landscaping. Runoff flows off-site
undetained to the western ally and conveyed via an existing gutter pan to the south
towards Emmaus Ln south of the site at Design Point 1.
Sub-basin B – consists of roof, pavement and a rain gardens. Runoff flows down the
private drive to a curb cut and into the rain garden. The rain garden outfalls into one of
the existing 18” RCP culverts under Blondel St at Design Point 2. The southern existing
culvert is to be abandoned by removing the end sections and approximately 14 ft of the
downstream end to ensure the remaining pipe is a minimum 1 ft below grade. The
remainder of the culvert shall be flowfilled. The northern culvert is to remain active and
will change ownership to the Ellie property for all future maintenance and repair.
Existing 18” Capacity:
80lf 18” RCP @ 0.2% capacity = 4.71 cfs. 100-year runoff for Basin B is 4.65 cfs and
therefore okay.
Final Drainage Report
Page 6 of 10
The Old Town North Third Filing drainage report (appendix D) indicates the culverts
were sized to accept 5.1 cfs while a 100-year event would overtop Blondel Street.
Sub-basin C – consists of sidewalks and landscaping. Runoff sheet flows into Sungia Rd
and into an existing storm inlet at the corner of Sungia Rd and Blondel St at Design Point
3.
Sub-basin D – consists of sidewalks and landscaping. Runoff sheet flows into Blondel St
at Design Point 4.
Point (acres) Runoff Runoff
b) There is no on-site detention required for this project. The subject property is within the Old
Town North Third Filing and 2009 NECCO study. The project runoff will be conveyed
through existing stormwater facilities to the NECCO detention pond north of Sungia Road.
NECCO assumed a 90% imperviousness (developed condition). The project’s proposed
imperviousness is 71%.
c) A rain garden is proposed within Basin B to treat a minimum of 75% of the new impervious
area. Site topography and the existing 18” RCP outfall limits the location of the rain garden
bottom requiring the use walls to obtain sufficient storage volume and provide 6 inches of
freeboard.
The rain garden has walls on all sides with a maximum height approximately of 3.5ft. The
eastern wall is flush with the grade. The lowest elevation of eastern the wall is approximately
31.6 feet long providing an emergency overflow to the east.
The rain garden volume was calculated using the MHFD UD-BMP (Version 3.07)
spreadsheet. The required WQCV = 654 cft including a factor of 1.2 from FCSCM equation
7-2. The rain garden is designed with a 12.25” ponding depth and provides 655 cft. The 4”
underdrain discharges into the outlet structure up to 12” below the outlet pipe. The outlet
structure is a 3 ft x 3 ft concrete box structure built over top the existing 18” RCP culvert
under Blondel Street.
d) LID techniques utilized in this design include the proposed rain garden.
Final Drainage Report
Page 7 of 10
e) Maintenance of the rain garden can be performed from the private drive or Blondel Street (20
ft east of the facility).
f) A drainage easement will be provided over the rain garden.
Maintenance of Bioretention (Rain Garden)
The primary maintenance objective for bioretention, also known as porous landscape
detention, is to keep vegetation healthy, remove sediment and trash, and ensure that the
facility is draining properly. The growing medium may need to be replaced eventually to
maintain performance. This section summarizes key maintenance considerations for
bioretention.
Inspection
Inspect the infiltrating surface at least twice annually following precipitation events to
determine if the bioretention area is providing acceptable infiltration. Bioretention facilities
are designed with a maximum depth for the WQCV of one foot and soils that will typically
drain the WQCV over approximately 12 hours. If standing water persists for more than 24
hours after runoff has ceased, clogging should be further investigated and remedied.
Additionally, check for erosion and repair as necessary.
Debris and Litter Removal
Remove debris and litter from the infiltrating surface to minimize clogging of the media.
Remove debris and litter from the overflow structure.
Mowing and Plant Care
a) All vegetation: Maintain healthy, weed-free vegetation. Weeds should be removed before
they flower. The frequency of weeding will depend on the planting scheme and cover. When
the growing media is covered with mulch or densely vegetated, less frequent weeding will be
required.
b) Grasses: When started from seed, allow time for germination and establishment of grass prior
to mowing. If mowing is required during this period for weed control, it should be
accomplished with hand-held string trimmers to minimize disturbance to the seedbed. After
established, mow as desired or as needed for weed control. Following this period, mowing of
native/drought tolerant grasses may stop or be reduced to maintain a length of no less than 6
inches. Mowing of manicured grasses may vary from as frequently as weekly during the
summer, to no mowing during the winter.
Irrigation Scheduling and Maintenance
a) Adjust irrigation throughout the growing season to provide the proper irrigation application
rate to maintain healthy vegetation. Less irrigation is typically needed in early summer and
Final Drainage Report
Page 8 of 10
fall, while more irrigation is needed during the peak summer months. Native grasses and
other drought tolerant plantings should not typically require routine irrigation after
establishment, except during prolonged dry periods.
b) Check for broken sprinkler heads and repair them, as needed. Completely drain the irrigation
system before the first winter freeze each year. Upon reactivation of the irrigation system in
the spring, inspect all components and replace damaged parts, as needed.
Sediment Removal and Growing Media Replacement
If ponded water is observed in a bioretention cell more than 24 hours after the end of a runoff
event, check underdrain outfall locations and clean-outs for blockages. Maintenance
activities to restore infiltration capacity of bioretention facilities will vary with the degree
and nature of the clogging. If clogging is primarily related to sediment accumulation on the
filter surface, infiltration may be improved by removing excess accumulated sediment and
scarifying the surface of the filter with a rake. If the clogging is due to migration of
sediments deeper into the pore spaces of the media, removal and replacement of all or a
portion of the media may be required. The frequency of media replacement will depend on
site-specific pollutant loading characteristics. Based on experience to date in the metro
Denver area, the required frequency of media replacement is not known. To date UDFCD is
not aware of any rain gardens constructed to the recommendations of these criteria that have
required full replacement of the growing media. Although surface clogging of the media is
expected over time, established root systems promote infiltration. This means that mature
vegetation that covers the filter surface should increase the life span of the growing media,
serving to promote infiltration even as the media surface clogs.
DRAINAGE DESIGN CRITERIA
a) The subject property is within the Old Town North Third Filing and 2009 NECCO study.
The project runoff will be conveyed through existing stormwater facilities to the NECCO
detention pond north of Sungia Road. NECCO assumed a 90% imperviousness (developed
condition). The proposed project site imperviousness is 71%. The previous studies have no
impact to the proposed design.
b) Four-step process
a. Where possible, the runoff sheet flows across landscaping before discharging into
Sungia Rd and Blondel St.
b. A rain garden is proposed to treat a minimum of 75% of the new impervious
pavement and roof areas.
c. There are no streams within the project area to strengthen.
d. A construction erosion control plan will be included with this project.
c) Rainfall data is provided in table 3.4.1 IDF Table for Rational Method from the Fort Collins
Stormwater Criteria Manual.
d) Design frequencies used in this design:
Minor: 2-year
Major: 100-year
Final Drainage Report
Page 9 of 10
e) The Rational method was used to calculate hydrological data following the Fort Collins
Stormwater Criteria Manual chapter 5.0The peak runoff from minor and major storm events
are calculated using the Rational Method formula as detailed below:
Q=CIA
Where:
Q= Storm runoff in cubic feet per second (cfs)
C= Runoff Coefficient (FCSCM ch. 5 sec. 3.2.2)
I = Runoff intensity in inches per hour
A= Drainage area in acres
Runoff coefficients were obtained from Table 3.2-2.
Times of concentration were calculated based on the initial time or overland flow time (for
urbanized undeveloped basins < 300’ overland flow), with a minimum time of concentration of 5
minutes.
t i =1.87(1.1 - C 5 )√L / S0.33 MANUAL Eqn. (3.3-2)
V =1.49/n R2/3S1/2 MANUAL Eqn. (5-4)
t t =L /(60V)MANUAL Eqn. (5-5)
t c =t i + t t MANUAL Eqn. (5-3)
MAX. t c =L/180 + 10 MANUAL Eqn. (3.3-5)
f) No on-site detention is required as part of this project.
g) No public streets requiring capacity calculations are required as part of this project.
h) The rain garden outlet structure is sized using weir flow calculations.
i) No storm sewer pipe networks are included with this project.
j) No swale or channels are included with this project.
k) No emergency spillways are included with this project. Should the pond overtop, the lowest
elevation of eastern the wall is approximately 31.6 feet long providing an emergency
overflow to the east.
VARIANCE REQUESTS
a) No variances are requested as part of this report.
EROSION CONTROL
a) This report is in compliance with all erosion control materials within the final Erosion
Control Report and Plans. An erosion control report is not required because the project
disturbance is under 1 acre.
CONCLUSION
a) Compliance with requirements – this design complies with the requirements of the city of
Fort Collins and master drainage plans referenced in this report.
Final Drainage Report
Page 10 of 10
b) Drainage plan effectiveness – this design effectively routes developed flows throughout the
site and provides water quality for at least 75% of the new impervious areas. This design
does not impact adjacent properties.
REFERENCES
1. City of Fort Collins Stormwater Criteria Manuel, December 2018.
2. Urban Storm Drainage Criteria Manual, Volumes 1, 2, and 3, Revised March 2024
3. North East College Corridor Outfall (NECCO), August 2009.
4. Old Town North Third Filing, Drainage, Sediment/Erosion Control, and Stormwater
Quality Report, June 2017
APPENDICES
A. Vicinity Map
B. FEMA Map
C. Soil Information
D. Old Town North Third Filing Excerpts
E. Drainage Calculations
F. Drainage Plans
Appendix A
National Flood Hazard Layer FIRMette
0 500 1,000 1,500 2,000250
Feet
Ü
SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT
SPECIAL FLOOD
HAZARD AREAS
Without Base Flood Elevation (BFE)
Zone A, V, A99
With BFE or DepthZone AE, AO, AH, VE, AR
Regulatory Floodway
0.2% Annual Chance Flood Hazard, Areas
of 1% annual chance flood with average
depth less than one foot or with drainage
areas of less than one square mileZone X
Future Conditions 1% Annual
Chance Flood HazardZone X
Area with Reduced Flood Risk due to
Levee. See Notes.Zone X
Area with Flood Risk due to LeveeZone D
NO SCREEN Area of Minimal Flood Hazard Zone X
Area of Undetermined Flood HazardZone D
Channel, Culvert, or Storm Sewer
Levee, Dike, or Floodwall
Cross Sections with 1% Annual Chance
17.5 Water Surface Elevation
Coastal Transect
Coastal Transect Baseline
Profile Baseline
Hydrographic Feature
Base Flood Elevation Line (BFE)
Effective LOMRs
Limit of Study
Jurisdiction Boundary
Digital Data Available
No Digital Data Available
Unmapped
This map complies with FEMA's standards for the use of
digital flood maps if it is not void as described below.
The basemap shown complies with FEMA's basemap
accuracy standards
The flood hazard information is derived directly from the
authoritative NFHL web services provided by FEMA. This map
was exported on 4/19/2024 at 2:17 PM and does not
reflect changes or amendments subsequent to this date and
time. The NFHL and effective information may change or
become superseded by new data over time.
This map image is void if the one or more of the following map
elements do not appear: basemap imagery, flood zone labels,
legend, scale bar, map creation date, community identifiers,
FIRM panel number, and FIRM effective date. Map images for
unmapped and unmodernized areas cannot be used for
regulatory purposes.
Legend
OTHER AREAS OF
FLOOD HAZARD
OTHER AREAS
GENERAL
STRUCTURES
OTHER
FEATURES
MAP PANELS
8
B 20.2
The pin displayed on the map is an approximate
point selected by the user and does not represent
an authoritative property location.
1:6,000
105°4'40"W 40°36'12"N
105°4'3"W 40°35'45"N
Basemap Imagery Source: USGS National Map 2023
Appendix B
Soil Map—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/19/2024
Page 1 of 3
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N
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 30 60 120 180
Feet
0 5 10 20 30
Meters
Map Scale: 1:627 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
Appendix C
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Map Unit Polygons
Soil Map Unit Lines
Soil Map Unit Points
Special Point Features
Blowout
Borrow Pit
Clay Spot
Closed Depression
Gravel Pit
Gravelly Spot
Landfill
Lava Flow
Marsh or swamp
Mine or Quarry
Miscellaneous Water
Perennial Water
Rock Outcrop
Saline Spot
Sandy Spot
Severely Eroded Spot
Sinkhole
Slide or Slip
Sodic Spot
Spoil Area
Stony Spot
Very Stony Spot
Wet Spot
Other
Special Line Features
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 18, Aug 24, 2023
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Jul 2, 2021—Aug 25,
2021
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Soil Map—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/19/2024
Page 2 of 3
Appendix C
Map Unit Legend
Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
73 Nunn clay loam, 0 to 1 percent
slopes
1.6 100.0%
Totals for Area of Interest 1.6 100.0%
Soil Map—Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/19/2024
Page 3 of 3
Appendix C
Larimer County Area, Colorado
73—Nunn clay loam, 0 to 1 percent slopes
Map Unit Setting
National map unit symbol: 2tlng
Elevation: 4,100 to 5,700 feet
Mean annual precipitation: 14 to 15 inches
Mean annual air temperature: 48 to 52 degrees F
Frost-free period: 135 to 152 days
Farmland classification: Prime farmland if irrigated
Map Unit Composition
Nunn and similar soils:85 percent
Minor components:15 percent
Estimates are based on observations, descriptions, and transects of
the mapunit.
Description of Nunn
Setting
Landform:Terraces
Landform position (three-dimensional):Tread
Down-slope shape:Linear
Across-slope shape:Linear
Parent material:Pleistocene aged alluvium and/or eolian deposits
Typical profile
Ap - 0 to 6 inches: clay loam
Bt1 - 6 to 10 inches: clay loam
Bt2 - 10 to 26 inches: clay loam
Btk - 26 to 31 inches: clay loam
Bk1 - 31 to 47 inches: loam
Bk2 - 47 to 80 inches: loam
Properties and qualities
Slope:0 to 1 percent
Depth to restrictive feature:More than 80 inches
Drainage class:Well drained
Runoff class: Medium
Capacity of the most limiting layer to transmit water
(Ksat):Moderately low to moderately high (0.06 to 0.20 in/hr)
Depth to water table:More than 80 inches
Frequency of flooding:None
Frequency of ponding:None
Calcium carbonate, maximum content:7 percent
Maximum salinity:Nonsaline (0.1 to 1.0 mmhos/cm)
Sodium adsorption ratio, maximum:0.5
Available water supply, 0 to 60 inches: High (about 9.1 inches)
Interpretive groups
Land capability classification (irrigated): 3e
Map Unit Description: Nunn clay loam, 0 to 1 percent slopes---Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/19/2024
Page 1 of 2
Appendix C
Land capability classification (nonirrigated): 4e
Hydrologic Soil Group: C
Ecological site: R067BY042CO - Clayey Plains
Hydric soil rating: No
Minor Components
Heldt
Percent of map unit:10 percent
Landform:Terraces
Landform position (three-dimensional):Tread
Down-slope shape:Linear
Across-slope shape:Linear
Ecological site:R067BY042CO - Clayey Plains
Hydric soil rating: No
Wages
Percent of map unit:5 percent
Landform:Terraces
Landform position (three-dimensional):Tread
Down-slope shape:Linear
Across-slope shape:Linear
Ecological site:R067BY002CO - Loamy Plains
Hydric soil rating: No
Data Source Information
Soil Survey Area: Larimer County Area, Colorado
Survey Area Data: Version 18, Aug 24, 2023
Map Unit Description: Nunn clay loam, 0 to 1 percent slopes---Larimer County Area, Colorado
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
4/19/2024
Page 2 of 2
Appendix C
Page 4
Drainage, Sediment/Erosion Control, and Stormwater Quality Report
Old Town North Third Filing; Fort Collins, Colorado
a. Runoff from the front lots of the single family lots fronting Osiander Street
and included in Sub -basin A is directed to the Old Town North detention
Pond. Refer to original Old Town North Drainage Plan in Appendix IV.
3. A majority of the Old Town North Third Filing property is included in the 2009
North East College Corridor Outfall (NECCO) study. Old Town North Third
Filing runoff will be conveyed to the NECCO detention Pond north of Suniga
Road via storm sewer.
a. A majority of the Old Town North Third Filing site is included in NECCO
Basin 810 and was modeled as a developed basin.
b. NECCO implemented an area of 8.2 acres for Basin 810 at 90%
imperviousness (developed condition) in the SWMM model.
4. A portion of the North East College Corridor Outfall (NECCO) improvements
were constructed adjacent to Old Town North Third Filing on the south side of
Suniga Road with the Aspen Heights Subdivision project to the north.
a. The section of storm sewer constructed in Suniga Road to convey runoff
from the south side of Suniga Road to the north side of Suniga Road is a
36" diameter RCP. The storm sewer profile included with the Aspen
Heights Subdivision Utility Plans is included with this report for immediate
reference. Refer to Appendix IV.
i. Reference Sheet 32 of 43 (record drawing) of the "Utility Plans for
Suniga Road to Blue Spruce Drive to Redwood Street and Redwood
Street from Lupine Drive to Cajetan Street" by Owen Consulting Group,
Inc.; Owen Project Number: 155-101FC; Plans dated April 29, 2015;
City Engineer approval date: 05/18/2015; Plan revision date:
10/28/2015 (As -Built storm).
b. The existing NECCO 36" RCP storm sewer is currently bulkheaded at both
ends with no outfall. Suniga Street existing inlets accept storm runoff and
snowmelt runoff to this section of storm sewer with no outfall. Therefore,
the NECCO 36" RCP storm sewer acts as a temporary storage facility.
There is approximately 960 LF of existing NECCO 36" RCP storm sewer
according to Sheet 32 of 43 (record drawing) of the "Utility Plans for Suniga
Road to Blue Spruce Drive to Redwood Street and Redwood Street from
Lupine Drive to Cajetan Street".
C. The NECCO Regional Detention Pond on the north side of Suniga Road is
not complete. It is currently built to accommodate Aspen Heights
Subdivision in an interim condition. Our understanding is that the NECCO
regional Pond and outfall will be completed in 2 to 4 years.
Apendix D
Project is part
of NECCO
Basin 810
Page 6
Drainage, Sediment/Erosion Control, and Stormwater Quality Report
Old Town North Third Filing; Fort Collins, Colorado
b. Refer to Aspen Heights Offsite Streets Sheet 30 of 43: Swale Plan and
Profile included in Appendix W.
C. Refer to Aspen Heights Offsite Streets Sheet 31 of 43: Swale Plan and
Profile included in Appendix IV.
3. Two (2) 14"x23" elliptical RCP culverts were placed under Blondel Street and a
channel was constructed on the Old Town north property with Aspen Heights
construction. Our understanding is that the culverts and channel were constructed
to convey interim historic flows from the west to Dry Creek and the Lake Canal.
Our understanding is that these flows are eliminated when the NECCO
improvements are completed.
a. The two (2) 14"x23" elliptical RCP culverts convey a 10-year storm flow
of 20.8 cfs.
b. The 50-year storm flow to this point is 35.8 cfs.
C. The 100-year storm peak flow is 46.8 cfs.
d. Refer to Appendix for April 27, 2015 e-mail from Larry Owen to Michael
Palizzi provided by Mr. Larry Owen discussing the Blondel Street culvert
capacity and interim peak flows.
4. After development of Aspen Heights Subdivision,construction of Suniga Road
and Redwood Street, and the construction of the interim channel on the Old Town
North property with the Aspen Heights Subdivision for conveyance of historic
flows from the west, runoff from a majority of the Old Town North Third Filing
site has no outfall. The channel berm was built up higher than existing grades on
the east and dammed the historic outfall point for this property.
a. Refer to Topographical Survey for Block 6, Tracts JJ and KK, Old Town
North by Intermill Land Surveying.
IV. DRAINAGE DESIGN CRITERIA
A. Regulations
Stormwater management improvements are designed in compliance with the
requirements of the City of Fort Collins Stormwater Criteria Manual adopted
December 2011. (Manual). The Manual incorporates most of the Urban Storm
Drainage Criteria Manual (USDCM) with amendments that are unique to Fort
Collins.
2. The latest versions of the USDCM software were used for runoff calculations.
Apendix D
Culverts no longer
required.
Page 11
Drainage, Sediment/Erosion Control, and Stormwater Quality Report
Old Town North Third Filing; Fort Collins, Colorado
C. Specific Details — Culverts and Channel
The two (2) 14"x23" elliptical RCP culverts that were placed under Blondel Street
with Aspen Heights construction will remain in place. Although identified as
temporary culverts in all Aspen Heights drawings, these culverts will most likely
remain in place, primarily to accommodate Tract F, Old Town North
redevelopment.
2. The two (2) 14"x23" elliptical RCP culverts that were placed under Redwood
Street with Aspen Heights construction will remain in place. No Old Town North
Third Filing runoff is directed to these culverts. They are there specifically for the
purpose of conveying historic flows prior to completion of the NECCO system
and could possibly be used if Lot 1, Block 12, Aspen Heights Subdivision is
developed. Flows from these culverts will be conveyed across the project through
the North Channel System.
3. The North Channel System consists of a trapezoidal channel with a 5' bottom
width and 4:1 side slopes. The channel has a main channel bed slope of 0.0039
ft/ft. The channel is sized to accommodate the required freeboard at QioVi.33 =
82.9 cfs. The resultant Froude Number = 0.50.
4. Pairs (2) of 18" NRCP culverts will be placed under the sidewalks that cross the
North Channel system. The culverts will not overtop during the 10yr event, and
will overtop 0.42' during the 100-year event. Please see the culvert calculations
in Appendix I.
D. Specific Detail — Street Capacities
The street capacities in Suniga Road upstream of Design Points 2, 3 and 3a are
not exceeded for either the Minor and Major storm events. The inlets installed on
Suniga Road are not to address capacity, but only to intercept the 100-year event
flow before it leaves the Project site. The inlet calculations are found in Appendix
I.
2. A typical cross section of the bump outs on Osiander Street was analyzed and the
street capacity was found to be 6.44 cfs to the crown elevation, satisfying both
the Minor and Major storm event requirements.
3. Emmaus Lane requires inlets at design points, 4, 4ac, 5 and 6 to address street
capacity and intercept the entire major storm event at the sag location located at
design point 4ac.
4. Street capacity calculations are presented in Appendix I.
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Apendix D
Project Location
FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5)
4.0 SWMM
4.1 Input Parameters
Page 11
Table 4.1-2. Land Use - Percent Impervious
Land Use
Percent Impervious
(%)
Residential
Urban Estate 30
Low Density 50
Medium Density 70
High Density 90
Commercial
Commercial 80
Industrial 90
Undeveloped
Open Lands, Transition 20
Greenbelts, Agriculture 2
Offsite Flow Analysis (when
Land Use not defined) 45
Reference: For further guidance regarding zoning classifications, refer to the Land Use
Code, Article 4.
For Final Plan (FP) submittals, impervious values must be based on the proposed land surface types.
Refer to Table 4.1-3 for recommended percent impervious values.
Table 4.1-3. Surface Type – Percent Impervious
Surface Type
Percent Impervious
(%)
Hardscape or Hard Surface
Asphalt, Concrete 100
Rooftop 90
Recycled Asphalt 80
Gravel 40
Pavers 40
Landscape or Pervious Surface
Playgrounds 25
Lawns, Sandy soil 2
Lawns, Clayey soil 2
Appendix ESite Imperviousness Calculations
TJC
Project Ellie
Date 12/19/2024
PAVEMENT 100%Table 3.2-2
ROOFS 90%Table 4.1-3
GRAVEL 50%Table 4.1-3
LANDSCAPE/UNDEVELOPED 2%Table 4.1-3
BASIN OVERALL
(ACRE)OVERALL (SF)PAVEMENT
(SF)
GRAVEL
(SF)ROOFS (SF) LANDSCAPE (SF) IMPERVIOUS
H1 0.81 35,197 - - - 35,197 2%
Site Total 0.81 35,197 - - - 35,197 2%
BASIN OVERALL
(ACRE)OVERALL (SF)PAVEMENT
(SF)
GRAVEL
(SF)ROOFS (SF) LANDSCAPE (SF) IMPERVIOUS
A 0.16 7,130 3,445 - 1,054 2,631 62%
B 0.47 20,348 6,146 - 13,534 668 90%
C 0.11 4,932 1,105 - - 3,827 24%
D 0.06 2,787 900 - - 1,887 34%
Site Total 0.81 35,197 11,596 - 14,588 9,013 71%
Impervious Calculation
T:\Projects\Ellie\03_Project Reports\Drainage\Calcs\C Calcx - Impervious 1/3/2025
Appendix E
Table 3.2-2. Surface Type - Runoff Coefficients
Asphalt, Concrete 0.95
Rooftop 0.95
Recycled Asphalt 0.80
Gravel 0.50
Pavers 0.50
Lawns, Sandy Soil, Flat Slope < 2% 0.10
Lawns, Sandy Soil, Avg Slope 2-7% 0.15
Lawns, Sandy Soil, Steep Slope >7% 0.20
Lawns, Clayey Soil, Flat Slope < 2% 0.20
Lawns, Clayey Soil, Avg Slope 2-7% 0.25
Lawns, Clayey Soil, Steep Slope >7% 0.35
3.2.1 Composite Runoff Coefficients
Drainage sub-basins are frequently composed of land that has multiple surface types or zoning
classifications. In such cases a composite runoff coefficient must be calculated for any given drainage
sub-basin.
The composite runoff coefficient is obtained using the following formula:
( )
t
n
i
ii
A
xAC
C
∑
==1 Equation 5-2
Where: C = Composite Runoff Coefficient
Ci = Runoff Coefficient for Specific Area (Ai), dimensionless
Ai = Area of Surface with Runoff Coefficient of Ci, acres or square feet
n = Number of different surfaces to be considered
At = Total Area over which C is applicable, acres or square feet
3.2.2 Runoff Coefficient Frequency Adjustment Factor
The runoff coefficients provided in Table 3.2-1 and Table 3.2-2 are appropriate for use with the 2-year
storm event. For any analysis of storms with higher intensities, an adjustment of the runoff coefficient is
required due to the lessening amount of infiltration, depression retention, evapotranspiration and other
losses that have a proportionally smaller effect on high-intensity storm runoff. This adjustment is
Appendix ESite Runoff Calculations
TJC
Project Ellie
Date 1/3/2025
PAVEMENT 0.95 Table 3.2-2
ROOFS 0.95 Table 4.1-3
GRAVEL 0.50 Table 4.1-3
LANDSCAPE/UNDEVELOPED 0.25 Table 4.1-3
BASIN OVERALL
(ACRE)OVERALL (SF)PAVEMENT
(SF)
GRAVEL
(SF)ROOFS (SF) LANDSCAPE (SF) 2 YR C 100 YR C
H1 0.81 35,197 - - - 35,197 0.25 0.30
Site Total 0.81 35,197 - - - 35,197 0.25 0.30
BASIN OVERALL
(ACRE)OVERALL (SF)PAVEMENT
(SF)
GRAVEL
(SF)ROOFS (SF) LANDSCAPE (SF) 2 YR C 100 YR C
A 0.16 7,130 3,445 - 1,054 2,631 0.69 0.86
B 0.47 20,348 6,146 - 13,534 668 0.93 1.00
C 0.11 4,932 1,105 - - 3,827 0.41 0.51
D 0.06 2,787 900 - - 1,887 0.48 0.60
Site Total 0.81 35,197 11,596 - 14,588 9,013 0.77 0.96
Total Imperviouss Area Added 26,184 SF
Min Area Treated (75% for RG)19,638 SF
Actual Area Treated 19,680 SF
OKAY!
"C" CALCULATIONS
T:\Projects\Ellie\03_Project Reports\Drainage\Calcs\C Calcx - C-CALCS 1/3/2025
Appendix E
TJC
Project Ellie
Date: 2/19/2025
ti = 1.87(1.1 - C5)√L / S0.33 MANUAL Eqn. (3.3-2)
V = 1.49/n R2/3S1/2 MANUAL Eqn. (5-4)
tt =L /(60V )MANUAL Eqn. (5-5)
tc = ti + tt MANUAL Eqn. (5-3)
MAX. tc =L/180 + 10 MANUAL Eqn. (3.3-5)
COMP FINAL REMARKS
AVG. SLOPE Tc Tc
Design Point BASIN(S) AREA C LENGTH AVG. SLOPE Ti LENGTH S n R VEL Tt TOTAL Tc=(L/180)+10
(Acres) (%) (ft/ft) (fps) (min) LENGTH (ft) (min) (min)
H1 H1 0.81 0.25 200 2.0 17.88 0.0 0.0 17.88 200 11.1 11.1
1 A 0.16 0.69 5.0 Use Min
2 B 0.47 0.93 5.0 Use Min
3 C 0.11 0.41 5.0 Use Min
4 D 0.06 0.48 5.0 Use Min
(Urbanized Basins)
TIME OF CONCENTRATION - DEVELOPED
SUB-BASIN DAT INITIAL / OVERLAND TRAVEL TIME (Tt)Tc CHECK
T:\Projects\Ellie\03_Project Reports\Drainage\Calcs\C Calcx - CONC. TIME 2/19/2025
Appendix E
Table 3.4-1. IDF Table for Rational Method
Duration
(min) 2-year 10-year 100-year
Duration
(min) 2-year 10-year 100-year
5 2.85 4.87 9.95
39 1.09 1.86 3.8
6 2.67 4.56 9.31
40 1.07 1.83 3.74
7 2.52 4.31 8.80
41 1.05 1.80 3.68
8 2.40 4.10 8.38
42 1.04 1.77 3.62
9 2.30 3.93 8.03
43 1.02 1.74 3.56
10 2.21 3.78 7.72
44 1.01 1.72 3.51
11 2.13 3.63 7.42
45 0.99 1.69 3.46
12 2.05 3.50 7.16
46 0.98 1.67 3.41
13 1.98 3.39 6.92
47 0.96 1.64 3.36
14 1.92 3.29 6.71
48 0.95 1.62 3.31
15 1.87 3.19 6.52
49 0.94 1.6 3.27
16 1.81 3.08 6.30
50 0.92 1.58 3.23
17 1.75 2.99 6.10
51 0.91 1.56 3.18
18 1.70 2.90 5.92
52 0.9 1.54 3.14
19 1.65 2.82 5.75
53 0.89 1.52 3.10
20 1.61 2.74 5.60
54 0.88 1.50 3.07
21 1.56 2.67 5.46
55 0.87 1.48 3.03
22 1.53 2.61 5.32
56 0.86 1.47 2.99
23 1.49 2.55 5.20
57 0.85 1.45 2.96
24 1.46 2.49 5.09
58 0.84 1.43 2.92
25 1.43 2.44 4.98
59 0.83 1.42 2.89
26 1.4 2.39 4.87
60 0.82 1.4 2.86
27 1.37 2.34 4.78
65 0.78 1.32 2.71
28 1.34 2.29 4.69
70 0.73 1.25 2.59
29 1.32 2.25 4.60
75 0.70 1.19 2.48
30 1.30 2.21 4.52
80 0.66 1.14 2.38
31 1.27 2.16 4.42
85 0.64 1.09 2.29
32 1.24 2.12 4.33
90 0.61 1.05 2.21
33 1.22 2.08 4.24
95 0.58 1.01 2.13
34 1.19 2.04 4.16
100 0.56 0.97 2.06
35 1.17 2.00 4.08
105 0.54 0.94 2.00
36 1.15 1.96 4.01
110 0.52 0.91 1.94
37 1.16 1.93 3.93
115 0.51 0.88 1.88
38 1.11 1.89 3.87
120 0.49 0.86 1.84
Appendix E
TJC
Project Ellie
Date: 2/19/2025 FALSE
DESIGN BASIN(S) AREA RUNOFF tc INTENSIT RUNOFF tc SUM INTENSIT RUNOFF DESIGN SLOPE PIPE LENGTH VEL Tt Tc
POINT (ACRES) COEFF (MIN) C*A (IN/HR) (CFS) (MIN) C*A (IN/HR) (CFS) Q (%) SIZE (FT) (FPS) (MIN) (MIN)
H1 H1 0.81 0.25 11.1 0.20 2.13 0.43
1 A 0.16 0.69 5.0 0.11 2.85 0.32
2 B 0.47 0.93 5.0 0.43 2.85 1.23
3 C 0.11 0.41 5.0 0.05 2.85 0.13
4 D 0.06 0.48 5.0 0.03 2.85 0.09
2 YR DESIGN STORM
2-YEAR DIRECT RUNOFF TOTAL RUNOFF TRAVEL TIME REMARKS
T:\Projects\Ellie\03_Project Reports\Drainage\Calcs\C Calcx - 2-Yr 2/19/2025
Appendix E
TJC
Project Ellie
Date: 2/19/2025 FALSE
DESIGN BASIN(S) AREA RUNOFF tc INTENSIT RUNOFF tc SUM INTENSIT RUNOFF DESIGN SLOPE PIPE LENGTH VEL Tt Tc
POINT (ACRES) COEFF (MIN) C*A (IN/HR) (CFS) (MIN) C*A (IN/HR) (CFS) Q (%) SIZE (FT) (FPS) (MIN) (MIN)
H1 H1 0.81 0.30 11.1 0.24 7.42 1.80
1 A 0.16 0.86 5.0 0.14 9.95 1.41
2 B 0.47 1.00 5.0 0.47 9.95 4.65
3 C 0.11 0.51 5.0 0.06 9.95 0.57
4 D 0.06 0.60 5.0 0.04 9.95 0.38
100 YR DESIGN STORM
100-YEAR DIRECT RUNOFF TOTAL RUNOFF TRAVEL TIME REMARKS
T:\Projects\Ellie\03_Project Reports\Drainage\Calcs\C Calcx - 100-Yr 2/19/2025
Appendix E
Analysis of Trapezoidal Channel (Grass-Lined uses SCS Method)
NRCS Vegetal Retardance (A, B, C, D, or E)A, B, C, D, or E =
Manning's n (Leave cell D16 blank to manually enter an n value)n = 0.012
Channel Invert Slope SO =0.0080 ft/f
Bottom Width B = 0.00 ft
Left Side Slope Z1 = 50.00 ft/ft
Right Side Sloe Z2 = 50.00 ft/ft
Check one of the following soil types:
Soil Type: Max. Velocity (MA ) Max Froude No. (FMA )
Non-Cohesive 5.0 fps 0.60
Cohesive 7.0 fps 0.80
Paved N/A N/A
Minor Storm Major Storm
Maximum Allowable Top Width of Channel for Minor & Ma or Storm TMAX = 20.00 20.00 f
Maximum Allowable Water Depth in Channel for Minor & Ma or Storm dMAX = 1.00 1.00 f
Allowable Channel Capacity Based On Channel Geometry Minor Storm Major Storm
MINOR STORM Allowable Capacity is based on Top Width Criterion Qallo = 4.8 4.8 cfs
MAJOR STORM Allowable Capacity is based on Top Width Criterion dallo = 0.20 0.20 f
Water Depth in Channel Based On Desi n Peak Flow
Desi n Peak Flow Qo = 1.3 4.7 cfs
Water Depth d = 0.12 0.20 ft
Ma or storm max. allowable capacity GOOD - reater than the desi n flow iven on sheet 'Inlet Mana ement'
MHFD-Inlet, Version 5.03 (Au ust 2023
REA INLET IN A SWALE
Drive Capacit
This worksheet uses the NRCS ve etal
retardance method to determine
Manning's n for grass-lined channels.
An override Manning's n can be
entered for other channel materials.
Minor storm max. allowable capacity GOOD - greater than the design flow given on sheet 'Inlet Management'
Choose One:
Non-Cohesive
Cohesive
Paved
MHFD-Inlet_v5.03, Drive Capacity 10/28/2024, 2:41 PM
Appendix E
Sheet 1 of 2
Designer:
Company:
Date:
Project:
Location:
1. Basin Storage Volume
A) Effective Imperviousness of Tributary Area, Ia Ia =90.0 %
(100% if all paved and roofed areas upstream of rain garden)
B) Tributary Area's Imperviousness Ratio (i = Ia/100)i = 0.900
C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.32 watershed inches
WQCV= 0.8 * 0.91* i3 - 1.19 * i2 + 0.78 * i
D) Contributing Watershed Area (including rain garden area)Area = 20,348 sq ft
E) Water Quality Capture Volume (WQCV) Design Volume VWQC =545 cu ft
Vol = (WQCV / 12) * Area
F) For Watersheds Outside of the Denver Region, Depth of d6 = in
Average Runoff Producing Storm
G) For Watersheds Outside of the Denver Region, VWQCV OTHER =cu ft
Water Quality Capture Volume (WQCV) Design Volume
H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER =cu ft
(Only if a different WQCV Design Volume is desired)
2. Basin Geometry
A) WQCV Depth (12-inch maximum)DWQC =12.25 in 12-INCH MAXIMUM
B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft
(Use "0" if rain garden has vertical walls)
C) Mimimum Flat Surface Area AMin =366 sq ft
D) Actual Flat Surface Area A ctual =642 sq ft
E) Area at Design Depth (Top Surface Area)Top =642 sq ft
F) Rain Garden Total Volume VT=655 cu ft
(VT= ((ATo + A ctual) / 2) * Depth)
3. Growing Media
Ft collins Det D-53 describes the media section
4. Underdrain System
A) Are underdrains provided?1
B) Underdrain system orifice diameter for 12 hour drain time
i) Distance From Lowest Elevation of the Storage y =0.0 ft
Volume to the Center of the Orifice
ii) Volume to Drain in 12 Hours Vol12 =545 cu ft
iii) Orifice Diameter, 3/8" Minimum DO = in
Design Procedure Form: Rain Garden (RG)
Jim Allen
TJC
January 3, 2025
Ellie
E Sungia & Blondel
UD-BMP (Version 3.07, March 2018)
Choose One
Choose One
18" Rain Garden Growing Media
Other (Explain):
YES
NO
Ellie RG Size, RG 1/3/2025, 10:21 AM
Appendix E
FCSCM EQ 7-2
WQCV = 545 X 1.2 = 654 CFT
VARIANCE REQ'D
NO ORIFICE PLATE
Sheet 2 of 2
Designer:
Company:
Date:
Project:
Location:
5. Impermeable Geomembrane Liner and Geotextile Separator Fabric
A) Is an impermeable liner provided due to proximity
of structures or groundwater contamination?
PROVIDE A 30 MIL (MIN) PVC LINER WITH CDOT CLASS B
GEOTEXTILE ABOVE IT. USE THE SAME GEOTEXTILE BELOW
THE LINER IF THE SUBGRADE IS ANGULAR
6. Inlet / Outlet Control
A) Inlet Control
7. Vegetation
8. Irrigation
A) Will the rain garden be irrigated?
Notes:
Design Procedure Form: Rain Garden (RG)
Jim Allen
TJC
January 3, 2025
Ellie
E Sungia & Blondel
Choose One
Choose One
Choose One
Sheet Flow- No Energy Dissipation Required
Concentrated Flow- Energy Dissipation Provided
Plantings
Seed (Plan for frequent weed control)
Sand Grown or Other High Infiltration Sod
Choose One
YES
NO
YES
NO
Ellie RG Size, RG 1/3/2025, 10:21 AM
Appendix E
RAIN GARDEN FOREBAY
TJC
Project The Elli
Date 2/19/202
VOLUME
Volume = 1% of Water Quality Capture Volume (WQCV)
WQCV = 545 Cft (per RG Calculations)
1% = 5.45 Cft
Depth = 1 ft
Min Area = 5 sft
Width for Shovel 2 ft
Min Length=2.725 ft
Use 3 ft x 3 ft = 9 SFT
Appendix E
RAIN GARDEN # 1
TJC
Project Ellie Townhomes Ft Collin
Date 10/28/202
Raingarden #1 Outlet Weir 3x3 Box Inlet
Step 1 Calculate head over weir at 2-yr runoff
Weir Flow
Qweir =C*L*H3/2
Solve for H
Where, 2 - Year
Qweir = discharge (cfs) =1.22
C = weir coefficient = 3.4
L = weir length (ft) = 9
H = head (ft) = 0.12
Step 2 Calculate head over weir at 100-yr runoff
Weir Flow
Qweir =C*L*H3/2
Solve for H
Where, 100 - Year
Qweir = discharge (cfs) =4.65
C = weir coefficient = 3.4
L = weir length (ft) = 9
H = head (ft) = 0.28
Appendix E
Pro ect:
P e ID:
Desi n Information In ut
Pipe Invert Slope So = 0.0020 ft/ft
Pipe Manning's n-value n = 0.0130
Pipe Diameter D = 18.00 inches
Design discharge Q = 4.65 cfs
1
Full-Flow Ca acit Calculated
Full-flow area Af = 1.77 sq ft
Full-flow wetted perimeter Pf = 4.71 ft
Half Central Angle Theta = 3.14 radians
Full-flow capacity Qf = 4.71 cfs
Calculation of Normal Flow Condition
Half Central Angle (0<Theta<3.14) Theta = 2.24 radians
Flow area An = 1.53 sq ft
Top width Tn = 1.18 ft
Wetted perimeter Pn = 3.35 ft
Flow depth Yn = 1.21 ft
Flow velocity Vn = 3.04 fps
Discharge Qn = 4.65 cfs
Percent of Full Flow Flow = 98.7% of full flow
Normal Depth Froude Number Frn = 0.47 subcritical
Calculation of Critical Flow Condition
Half Central Angle (0<Theta-c<3.14)Theta-c = 1.68 radians
Critical flow area Ac = 1.00 sq ft
Critical top width Tc = 1.49 ft
Critical flow depth Yc = 0.83 ft
Critical flow velocity Vc = 4.65 fps
Critical Depth Froude Number Frc = 1.00
CIRCULAR CONDUIT FLOW Normal & Critical De th Com utation
Ellie TH
Existin 18" RCP
MHFD-Culvert, Version 4.00 Ma 2020
MHFD-Culvert_v4.0, Pipe 6/18/2024, 4:05 PM
Appendix E
Capacity check for rain
garden outfall through
existing 18" RCP.
Stormwater Facility Name:
Facility Location & Jurisdiction:
User Input: Watershed Characteristics User Defined User Defined User Defined User Defined
Selected BMP Type = RG Stage [ft] Area [ft^2] Stage [ft] Discharge [cfs]
Watershed Area = 0.47 acres 0.00 642 0.00 0.01
Watershed Length =250 ft 1.00 642 1.00 0.02
Watershed Length to Centroid = 120 ft 1.10 642 1.10 4.65
Watershed Slope =0.010 ft/ft 1.20 642 1.20 10.00
Watershed Imperviousness = 92.0%percent
Percentage Hydrologic Soil Group A = 0.0%percent
Percentage Hydrologic Soil Group B = 0.0%percent
Percentage Hydrologic Soil Groups C/D = 100.0%percent
Target WQCV Drain Time = 12.0 hours
User Input
After completing and printing this worksheet to a pdf, go to:
https://maperture.digitaldataservices.com/gvh/?viewer=cswdif
Create a new stormwater facility, and attach the PDF of this
worksheet to that record.
Routed Hydrograph Results
Design Storm Return Period =WQCV 2 Year 5 Year 10 Year 50 Year 100 Year
One-Hour Rainfall Depth =N/A 2.85 3.00 4.87 5.00 9.95 in
CUHP Runoff Volume =0.013 0.107 0.113 0.189 0.194 0.394 acre-ft
Inflow Hydrograph Volume =N/A 0.107 0.113 0.189 0.194 0.394 acre-ft
Time to Drain 97% of Inflow Volume =10.9 11.4 11.3 9.3 9.1 4.6 hours
Time to Drain 99% of Inflow Volume =11.2 13.7 13.7 12.9 12.8 10.9 hours
Maximum Ponding Depth =0.89 1.06 1.07 1.06 1.09 1.14 ft
Maximum Ponded Area =0.01 0.01 0.01 0.01 0.01 0.01 acres
Maximum Volume Stored =0.013 0.016 0.016 0.016 0.016 0.017 acre-ft
Once CUHP has been run and the Stage-Area-Discharge
information has been provided, click 'Process Data' to
interpolate the Stage-Area-Volume-Discharge data and
generate summary results in the table below. Once this
is complete, click 'Print to PDF'.
Stormwater Detention and Infiltration Desi n Data Shee
Bioretention Pond
Blondel and Suniga
SDI-Design Data v2.00, Released January 2020
Location for 1-hr Rainfall Depths (use dropdown):
After providing required inputs above including 1-hour
rainfall depths, click 'Run CUHP' to generate runoff
hydrographs using the embedded Colorado Urban
Hydrograph Procedure.
SDI_Detention System, Design Data 10/28/2024, 2:42 PM
Appendix E
Booleans for Message Booleans for CUHP
Watershed L:W 1 CUHP Inputs Complete
Watershed Lc:L 1 CUHP Results Calculated
Watershed Slope FALSE Time Interval
RunOnce 1
CountA 1
Draintime Coeff 0.8
User Precip 1
Equal SA Inputs 1
Equal SD Inputs 1
Stormwater Detention and Infiltration Desi n Data Shee
0
1
2
3
4
5
6
7
8
0.1 1 10
FL
O
W
[
c
f
s
]
TIME [hr]
100YR IN
100YR OUT
50YR IN
50YR OUT
10YR IN
10YR OUT
5YR IN
5YR OUT
2YR IN
2YR OUT
WQCV IN
WQCV OUT
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0.1 1 10 100
PO
N
D
I
N
G
D
E
P
T
H
[
f
t
]
DRAIN TIME [hr]
100YR
50YR
10YR
5YR
2YR
WQCV
SDI_Detention System, Design Data 10/28/2024, 2:42 PM
Appendix E